1. Field of the Invention
The invention generally relates to a breathable, waterproof textile laminate. More specifically, the invention relates to textile laminates useful in the production of apparel, industrial, military, and medical products, and the like, which are resistant to contamination, thereby retaining breathability and waterproofness throughout use and numerous cleaning, laundering, or restoration cycles. The invention also relates to a method of producing such a laminate.
2. Description of the Prior Art
Breathable waterproof textile laminates are beneficial in a myriad of applications. For example, breathable waterproof textile laminates are useful in a range of apparel, industrial, medical, and military applications. More particularly, breathable waterproof textile laminates are useful in articles of apparel such as uniforms, workwear, outerwear, active wear, and protective clothing. Beneficial industrial applications include uses such as filtration. Medical applications for breathable waterproof laminates include uses such as surgical drapes and cast linings. Military applications include use in tents, tarps, and such. Other applications for such laminates include but are not limited to use in mattress pads and animal protective wear.
Breathable waterproof laminates are particularly advantageous in traditional textile fabric applications, such as apparel. Conventional textile fabric which is designed to be waterproof often tends to be uncomfortable to the user, because moisture given off by the body is generally retained within the interior space defined by the textile fabric and thus remains adjacent the user""s body. This represents a particular problem to those users who are active while in a moist or wet environment and in those environments which are warm as well as wet, since the incidence of user perspiration therefore is increased.
Retained moisture is particularly problematic in textile fabrics worn as garments. For example, military personnel, sportsmen and athletes often find the discomfort due to perspiration trapped within their garments to be particularly acute. Therefore, garments are often provided with vents in locations on the garment where it is perceived to be less critical that full waterproofness be provided. For example, vents are often provided underneath the arms of garments (i.e. in the armpit region) or beneath flaps provided in the garment. As will be readily recognized, however, such vents only enable moisture to escape from localized areas within the garment, and the passage is still often inadequate to insure complete wearer dryness and comfort. Furthermore, the provision of such vents requires specially-configured garments which can be more expensive to produce, and the integrity of the waterproofness of the garment can be diminished due to the vent openings.
It is now recognized that, rather than utilizing air vents, merely transporting the water vapor contained in perspiration away from the user provides adequate comfort. A textile fabric""s ability to transport water vapor through its thickness is commonly referred to as its xe2x80x9cbreathability.xe2x80x9d Although generally more comfortable, breathable materials often provide unacceptable levels of waterproofness, as the ability of a textile fabric to prevent the passage through of liquid water generally tends to be inversely proportional to the high moisture vapor transmission rate characteristic of breathable fabrics.
However, textile fabric constructions have been developed which attempt this difficult balance between breathability and waterproof properties. In general, these constructions are laminates incorporating a polymeric film, also referred to as a membrane. The primary purpose of the film layer is to repel liquid water without sacrifice to breathability. Two types of waterproof breathable films are currently available: solution-diffusion films and porous diffusion films.
Solution-diffusion films are extremely hydrophilic films which xe2x80x9csolubilizexe2x80x9d water vapor within their molecular chains. These films transport individual water molecules through their thickness by molecular diffusion. Solution-diffusion films are nonporous, thus providing the additional benefit of air-impermeability, or xe2x80x9cwindproofness.xe2x80x9d Although breathable and waterproof, the hydrophilic nature of solution-diffusion films cause them to swell and weaken significantly when in prolonged contact with liquid water. Therefore, solution-diffusion films usually exhibit poor durability. The problems encountered in the use of solution-diffusion films are discussed extensively in U.S. Pat. No. 5,660,198.
In contrast, porous diffusion films, commonly referred to as microporous films, are hydrophobic in nature. Porous diffusion films are generally characterized by a network of interconnecting pores which span the thickness of the film. These pores are too small to allow liquid water to pass, but are large enough to permit water vapor to readily flow through. Expanded polytetraflouroethylene film (xe2x80x9ce-PTFExe2x80x9d) is a particularly widely known example of such a microporous film. Unfortunately, although microporous films do retain their physical integrity over time, they too lack durability for another reason. Porous diffusion films are adversely affected by exposure to surface active agents present during wear or laundering. For example, surface active agents present in perspiration, such as body oils, salts, and the like, penetrate the microporous membrane over time, coating its pores and causing it to lose its waterproof characteristics.
Coatings have been used to protect the pores of microporous films, in particular e-PTFE films. These coatings are applied to the microporous membrane as either a continuous layer of a liquid solution or a molten application. Although providing protection, coatings penetrate the surface of the microporous film and stiffen the resulting laminate. Several coated microporous membranes are marketed by W. L. Gore and Associates, Inc., under the tradename GORETEX. Examples of coated e-PTFE fabrics are described in U.S. Pat. Nos. 4,194,041 to Gore et al. and 5,026,591 to Henn et al, the disclosures of which are incorporated herein by reference. It is also generally known to bond e-PTFE membranes to a thick, protective film using an adhesive; however, the use of thick protective films likewise increases the stiffness of the resulting laminate. Increasing the stiffness adversely affects the drape, i.e., the feel and flexibility in all directions, of the resulting fabric.
Further, the manner in which the layers comprising the waterproof breathable laminate are joined also affects the performance of the resulting fabric structure. In particular, the layers within the laminate must be cohesive, i.e. move in unison upon flexing. This unitary flexing is especially important in fabrics subjected to pressure testing, such as fabrics for use in military applications. In particular, it is important that the laminate layers act in unison in fabrics subjected to hydrostatic testing.
To provide a cohesive laminate, it is known to use adhesives, in particular nonbreathable adhesives, to bond the layers together. However, by definition, nonbreathable adhesives, although highly durable, detract from the overall performance of the product by lowering the moisture vapor transmission rate of the resulting laminate. The use of such nonbreathable adhesives in conjunction with hydrophilic films is taught in U.S. Pat. Nos. 5,660,918 and 4,761,324.
Breathable adhesives are available for use in waterproof fabric laminates. However, caution must be taken in their use, as well. Breathable adhesives are hydrophilic in nature. Similar to solution-diffusion films, breathable adhesives lack durability due to their tendency to swell with water and subsequently weaken over time. This issue is especially problematic when bonding stretch resistant materials, which do not yield, or give, when the adhesive swells. The use of breathable adhesives presents particular difficulties in those applications involving launderability standards. Further, as with any coating, the use of excessive amounts of adhesive, breathable or otherwise, results in a stiffer fabric laminate.
As indicated above, a wide variety of competing factors affect the overall performance of waterproof, breathable laminates, requiring a difficult balance to be struck to provide an optimal fabric structure. There remains a need for a fabric construction having a high degree of breathability and waterproofness, which resists contamination during wear, cleaning, laundering, and restoration processes, which is durable and possesses superior drape. Furthermore, a need exists for a process for making such a material in an efficient and cost effective manner.
The present invention combines the advantages of solution-diffusion films, porous diffusion films, durable adhesives, and breathable adhesives to create a unique textile laminate for use in outdoor garments and other textile applications. The textile laminates of the present invention exhibit many advantageous properties. For example, the textile laminates of the present invention are extremely breathable, have superior waterproof properties, have excellent drape, are soft to the touch, and are quiet. The present invention further provides a method by which to produce the breathable waterproof textile laminate of the present invention.
More particularly, the present invention provides a breathable waterproof textile laminate containing a minimum of two layers formed by adhering a microporous membrane to a nonporous layer capable of diffusing water vapor through its thickness. In one advantageous embodiment, a face layer is further adhered to the microporous membrane component, thus providing a three layer laminate. Both durable, i.e. nonhydrophilic, and breathable, i.e. hydrophilic, adhesives are used within the construction to impart cohesion to the laminate structure. In another aspect of this advantageous embodiment, a backing layer is further adhered to the nonporous layer component, using either a breathable hydrophilic adhesive or a durable nonhydrophilic adhesive, thus forming a four layer laminate. In an alternative embodiment, a three layer laminate comprised of a backing layer adhered to the nonporous film component in a nonporous film/microporous membrane laminate is provided.
In one advantageous embodiment, the face layer is a durable woven nylon fabric, preferably having a fabric weight ranging from about 1 to about 10 ounces/yd2. Exemplary microporous membranes for use in the present invention include expanded polytetraflouroethylene and similar films. Expanded polytetraflouroethylene (e-PTFE) is employed in a particularly advantageous embodiment of the present invention. The e-PTFE may be further characterized as having an air permeability of from about 0.5 to about 7.0 ft3/min, and is preferably from about 25 to about 75 microns thick. In one advantageous embodiment, the nonporous layer has a moisture vapor transmission rate of from about 3000 to about 5000 gm/m2/24hr. In a further aspect of the invention, the nonporous layer has a thickness of from about 5 to about 25 microns. In a preferred embodiment, the nonporous layer is a nonporous film. Exemplary nonporous films include polyether polyurethane.
The layers are adhered using a combination of breathable hydrophilic adhesives and durable nonhydrophilic adhesives. Exemplary breathable hydrophilic adhesives include polyether polyurethane. In one advantageous embodiment, polyether polyurethane is employed to adhere the microporous membrane to the nonporous layer. In a further embodiment, a breathable hydrophilic adhesive is used to bond the nonporous layer to the backing layer.
The durable nonhydrophilic adhesive may also be a variety of materials, including crosslinkable polyester polyurethane. In a preferred embodiment, crosslinkable polyester polyurethane is employed to bond the face layer to the microporous membrane, particularly in those embodiments in which the face layer is comprised of a stretch resistant construction.
The adhesives of the present invention are generally applied in a discontinuous pattern. In one advantageous aspect of the present invention, adhesive covers from about 40 to about 50% of the bonding surface between the face layer and the microporous membrane, applied in an amount ranging from about 0.25 to 0.35 oz/yd2. In a further advantageous aspect, the adhesive applied between the microporous membrane and the nonporous layer, as well as that applied between the nonporous layer and the backing layer, covers about 40% to about 50% of the respective bonding surfaces, and is applied in an amount ranging from about 0.25 to 0.35 oz/yd2.
In further embodiments, methods to form the novel laminates of the present invention are provided. These methods include advancing a pair of layers adjacent to each other and adhering them. In further aspects of the invention, the adhesion process comprises applying the adhesive using gravure coating. The layers may be further dried and/or cured as part of the adhesion process.
The present invention provides a waterproof, breathable fabric laminate having superior durability and drape by combining the advantages of several materials. In particular, the durable fabric of the present invention is able to withstand the rigors of use, cleaning, laundering, and restoration. In addition, the present invention provides a soft fabric, which is quiet. The present invention provides the foregoing benefits by utilizing a combination of waterproof, breathable materials in conjunction with a combination of adhesives to provide superior overall performance.